Ovens for domestic use today employ a wide variety of cooking methods. The most common types of ovens are the conventional electric and gas ovens which cook the food by radiant heat.
In cooking with an oven, a principal objective is frequently (for example, when baking) to achieve a substantially uniform temperature throughout the interior of the oven chamber as the quality and "doneness" of the cooked food product is closely related to the uniformity of interior oven temperature. A problem with conventional ovens is often the nonuniformity of the temperature within the oven chamber. Conventional ovens typically have a natural hot air flow pattern dictated by the interior geometry of the oven that results in uneven heating within the oven chamber and food that is not cooked uniformly. Thus, it is important to achieve substantially uniform heating of the oven cooking chamber.
Convection ovens employ a blower means in the oven chamber to circulate air at elevated velocities within the oven chamber to improve heat distribution and the effectiveness of the heating elements and to reduce the cooking time. In many cooking situations, there is often a layer of air adjacent the surface of the food being cooked and/or the cooking utensils which provides, in effect, a thermal barrier that retards the cooking process. The increased circulation of heated air that may result from forced air flow may eliminate this barrier, thereby facilitating the transfer of heat to the food and resulting in faster cooking times. In addition, the circulation of heated air within the oven chamber generally improves the temperature uniformity within the oven and contributes to more even cooking.
Prior attempts at providing an effective convection oven are numerous. U.S. Pat. No. Re. 26,063 (originally U.S. Pat. No. 3,074,393) discloses an oven provided with a blower-and-motor assembly mounted adjacent the rear wall in the interior of the oven chamber. A baffle plate positioned in front of the blower is formed with a central aperture which permits air to flow axially into the blower impeller which, in turn, expels the air radially outwardly, in a turbulent manner, toward the sides, top and bottom walls of the oven chamber as directed by the baffle plate.
U.S. Pat. No. 4,010,341 discloses a well-type oven equipped with a fan, a heater and a plurality of circulation passages. The oven of the '341 patent comprises a well which is positionable within a counter or similar support, is open at the top, and has a removable insert disposed therein defining, together with the well, the circulation passages. The fan and the heater are positioned in the lower side of a lid that is removably fitted over the well to define a top closure for the oven.
U.S. Pat. No. 4,687,908 discloses a portable, self-contained convection blower for use with conventional ovens. The portable electric blower may be placed on the floor of the oven to circulate heated air throughout the oven chamber.
U.S. Pat. No. 4,484,063 describes a convection oven having an air-distribution chamber disposed above the main cooking compartment. The oven of the '063 patent includes a centrifugal fan disposed behind a diffuser panel which is provided with discharge openings of non-uniform size and asymmetrical patterns. The discharge openings are so arranged to take advantage of the oven geometry in an attempt to achieve uniform heating of the cooking compartment with a closed-air circulation system.
U.S. Pat. No. 4,813,398 discloses a gas-fired convection oven comprising a blower fan mounted on the rear wall of the interior of the cooking chamber. A vertical shroud is mounted adjacent the fan opposite of the rear wall to form a narrow heat-exchanging chamber within the oven chamber. The vertical shroud is formed with a partially baffled, centrally disposed air opening to ensure that each of the two legs of a heat exchanger receive approximately equal portions of combustion air and gas such that uniform heating of the heat exchanger is possible in an attempt to achieve better heat distribution throughout the interior of the cooking chamber.
U.S. Pat. No. 4,829,158 discloses a portable electric convection oven having a blower means provided in a side wall of the oven housing. The interior of the oven is organized with a central food receiving area spaced between upper and lower air-distribution plenums. Separating the plenums and the central food receiving area are two removable air-distribution plates that are provided with formed perforations therein that define nozzles to direct the heated air against the food products.
Attempts have also been made to position a fan means within the door of a dishwasher for circulating air within the washing chamber during the drying cycle. Exemplary of such attempts are U.S. Pat. Nos. 3,068,877 and 3,908,681.
U.S. Pat. No. 3,068,877 describes a dishwasher door having a first conduit located within the door in communication with the dishwasher chamber and a second conduit in communication with the atmosphere and in heat exchange relationship with the first conduit. The door of the '877 dishwasher further includes a blower system driving a first impeller disposed in the first conduit for recirculating vapor from the dishwashing chamber and a second impeller disposed in the second conduit for circulating cooling air from the atmosphere.
U.S. Pat. No. 3,908,681 describes a forced-air circulation system for a dishwasher, incorporating a fan-and-motor assembly mounted within the dishwasher door for circulating air downwardly through the wash chamber during the drying cycle.
As noted above, forced convection ovens generally offer an advantage over conventional ovens in their reduction of cooking times by more uniform heat transfer to the food product. With prior ovens, forced circulation systems were formed in the walls of the oven chambers where the blower and motor were relatively inaccessible and their location exposed them to the high temperatures of the oven chamber and required relatively expensive motors and insulating structures designed for high temperature operation. Furthermore, location of the forced circulation system within the oven reduced the interior capacity of the oven chamber.